A data processing system may include hardware resources such as a processing unit (CPU), volatile memory (RAM) and non-volatile memory (ROM). The data processing system may operate under the control of at least one operating system and may perform routines according to one or several software resources or applications. The applications may be stored in non-volatile memory and loaded into volatile memory when required to be executed. During the execution of an application, the data required by said application or the data which is produced by the application may be stored in the non-volatile or volatile memory or transferred from one memory to another.
With the advent of multiple connectivity options for data processing systems, including wireless connectivity, and with the huge growth in the use of mobile data processing systems, the need to protect these systems from malicious attacks has become increasingly important. Malicious attacks can be aimed at interfering with system booting, modifying the operating system, intercepting and/or modifying data produced by or utilized by some application.
Indeed, it has now become a necessary requirement to protect data processing systems against fraudulent manipulations and attacks on their integrity. Such malicious attacks may come in the form of software designed to take over a data processing system's operating system or otherwise interfere with the normal processing sequence of the data processing system without the user's knowledge or approval. Such software is generally known as malware. The presence of malware in a data processing system is generally difficult to remedy and can lead to complete system failure or even to irreparable damage to the system.
Computer viruses, worms, Trojan horses, spyware etc. are all different types of malware. The different types of malware can attack the processing system in various ways such as by intercepting data which was meant for another application or by monitoring key strokes in order to steal passwords or other information which is meant to be kept secret, modifying or otherwise altering data or corrupting files, modifying a program in order to cause it to crash or to execute some function which was not originally intended by the user.
Systems to combat against malware attacks exist and usually feature a memory management unit, which is configurable by the system's CPU. Security is thus compromised if the CPU suffers an attack from an ill-intentioned user. Because of the complexity exhibited by a modern CPU, the additional security functions which would be required in order to minimize the possibility of such an attack would lead to a significant cost increase in terms of the extra on-chip real estate necessary to implement such functions and would lead to computing overhead and therefore compromise the speed of operation. Again, due to the complexity of a typical CPU, such modifications could not offer a high level of security with an acceptable level of confidence. Accordingly, it would be desirable to have a cost-efficient and size-efficient solution providing secure management of the loading or unloading of data or applications into or out of memories in a data processing system.
A secure memory management unit for a microprocessor is described in U.S. Pat. No. 5,825,878. This document discloses the use of a secure embedded memory management unit for a microprocessor for transferring encrypted data and encrypted instructions from an external memory. Security is afforded by the fact that the direct memory access controller is embedded on the same chip as the microprocessor, making it difficult for a malicious third party to gain access to instructions and commands from within the microprocessor chip itself, where the signals are in clear. No means for ensuring that the data in the embedded memory is only accessed by an authorised processor operating in a particular mode. As such, there is still a possibility for an unscrupulous party to replace memory content by malicious content.
U.S. Patent Application Publication No. 2003/0,037,220 A1 discloses an MMU (memory management unit) which uses segmentation addressing, whereby stored data comprises a segment descriptor. The segment descriptor is used to allow ease of address mapping. The presence of the segment descriptor simplifies the address mapping thereby eliminating the need for a separate loader. This does not therefore address any particular security-related problem.